System and method for three dimensional model printing

ABSTRACT

A scanning 3-D printing system comprises a printing platform movable in a printing direction and in an indexing direction, the printing platform comprising a printing head configured for dispensing building material while the printing platform is moving in a printing direction one pass at a time, and layer by layer, a roller configured for leveling the dispensed building material one pass at a time, wherein the roller is rotatably mounted on a roller axle, and wherein the roller axle extends over all passes of the printing system and is stationary in the indexing direction, a scraper configured for scraping excess building material off the roller, and a trough configured for collecting the building material scraped off the roller.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/834,457 filed on Aug. 25, 2015 which is a division of U.S. patentapplication Ser. No. 12/937,274 filed on Oct. 11, 2010, now U.S. Pat.No. 9,132,587, which is a National Phase of PCT Patent Application No.PCT/IL2008/000501 having International Filing Date of Apr. 10, 2008. Thecontents of the above applications are all incorporated by reference asif fully set forth herein in their entirety.

FIELD OF THE INVENTION

The present invention, in some embodiments thereof, relates to the fieldof Solid Freeform Fabrication (SFF) and more particularly but notexclusively to raster scanning three-dimensional (3-D) printing systems.

BACKGROUND OF THE INVENTION

Solid freeform fabrication (SFF) is a known technique for manufacturingsolid objects, for example by the delivery of material and optionallyenergy to specified points in space to produce the solid object.Typically, the object is built in layers corresponding to virtual crosssections of the object from a CAD model.

One of the methods for SFF includes 3-D printing.

In U.S. Pat. No. 6,259,962 entitled “Apparatus and method for threedimensional printing”, assigned to the common assignee and incorporatedherein by reference in its entirety, describes an apparatus and a methodfor 3-D model printing. U.S. Pat. No. 6,259,962 describes an apparatusincluding a printing head having a plurality of nozzles, a dispenserconnected to the printing head for selectively dispensing interfacematerial in layers and curing means for optionally curing each of thelayers deposited. The depth of each deposited layer is controllable, byselectively adjusting the output from each of the plurality of nozzles.

Typically, the 3-D object is formed on a tray, which may be movable inat least a direction perpendicular to the building plane (Z direction).To reduce cost and maintenance expenses, some systems as described forexample in U.S. Pat. No. 6,259,962, include a printing head withdimensions that are shorter than the dimensions of the tray or objectand performs sequential raster scanning of the tray, one pass after theother, to form each of the layers.

U.S. Patent Application Publication No. 20050104241, entitled “Apparatusand method for three dimensional model printing” assigned to the commonassignee and incorporated by reference in its entirety, describes anobject correcting apparatus to alter the thickness of a layer of thedispensed material to a pre-determined height. The object correctingapparatus may include, for example, a roller and a cleaning apparatus toremove material from the roller. The roller may operate at selectedspeeds and directions, and may be heated and/or cooled, to help ineffectively altering dispensed material.

According to embodiments described in U.S. Pat. No. 6,850,334 and U.S.Patent Application Publication No. 20050104241, the 3-D printing systemsmay include a printing head having a dispensing unit with a plurality ofnozzles through which material may be selectively dispensed, a rollerunit for removing surplus material from each layer and a curing unit forcuring the interface material of each layer to form the 3-D object. Theroller unit may include a roller for leveling the material as well as ascraper and trough for scraping and collecting excess building materialoff the roller. The roller unit in this case is conformed to thedimensions of the printing head.

Typically, the printing head may be movably supported on a planeparallel to the building plane. The printing head is advanced along aprinting direction (X direction) to print each pass and then shiftedalong an indexing direction (Y direction) to print subsequent passes,substantially on the same plane. The roller is rotatably engaged on theprinting head such that its longitudinal axis is parallel to theindexing direction and rotates in a direction “opposite” to thedirection of printing due to the friction between the roller and thesurface. Typically, a motor engaged on the roller, facilitates rotationof the roller.

Typically during raster scanning printing, the printing head dispensesmaterial over a pass, levels that pass with the roller to remove anysurplus material over that pass, and then cures that pass. This processis repeated for each pass and over all the layers until the 3-D objectsare completed.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the present invention is the provisionof a raster scanning 3-D printing system that provides seamless levelingbetween adjacent passes in a printing layer.

An aspect of some embodiments of the present invention, is the provisionof a raster scanning 3-D printing system comprising a printing platformmovable in a printing direction and in an indexing direction, theprinting platform comprising a printing head configured for dispensingbuilding material while the printing platform is moving in a printingdirection one pass at a time, and layer by layer, a roller configuredfor leveling the dispensed building material one pass at a time, whereinthe roller is rotatably mounted on a roller axle, and wherein the rolleraxle extends over all passes of the printing system and is stationary inthe indexing direction, a scraper configured for scraping excessbuilding material off the roller, and a trough configured for collectingthe building material scraped off the roller.

Optionally, the roller axle is supported on a Y rail aligned with theindexing direction, wherein the Y rail is mounted at each end to acarriage, wherein the carriage is configured to support and couple the Yrail on each of its ends to an X rail aligned with the printingdirection.

Optionally, the carriage is movable in the printing direction.

Optionally, the roller extends over all passes of the printing systemand is stationary in the indexing direction.

Optionally, the scraper is movable in the indexing direction.

Optionally, the scraper is mounted on the printing platform.

Optionally, the trough is movable in the indexing direction.

Optionally, the trough is mounted on the printing platform.

Optionally, the printing platform is configured for offsetting thescraper's position in the indexing direction for printing differentlayers.

Optionally, the scraper and the trough extend over the entire length ofthe roller axle and are stationary in the indexing direction.

Optionally, the system comprises at least two conduits distributed alongthe trough and configured for removing the building material collectedin the trough.

Optionally, comprises a pump configured for pumping off the buildingmaterial collected in the trough, wherein the building material ispumped out of the trough from above the trough.

Optionally, a tray configured for supporting the dispensed buildingmaterial at a defined height, wherein the tray is movable in a verticaldirection, wherein the vertical direction is perpendicular to theprinting direction and the indexing direction.

An aspect of some embodiments of the present invention is the provisionof a method for printing 3-D objects with a raster scanning 3-D printingsystem, the method comprising dispensing building material from aprinting platform while moving in a printing direction one pass at atime and layer by layer, shifting the printing platform in an indexingdirection prior to dispensing a subsequent pass of a layer, and levelingthe building material after each dispensing with a roller, wherein theroller is rotatably mounted on a roller axle, and wherein the rolleraxle extends over all passes of the printing system, is stationary inthe indexing direction and is movable in the printing direction.

Optionally, the method comprises shifting the roller in the indexingdirection after leveling a pass in a layer.

Optionally, the roller extends over all printed passes of the printingsystem.

Optionally, the method comprises at least one of a scraper configuredfor scraping excess building.

Optionally, the roller and a trough configured for collecting thebuilding material scraped off the roller are mounted on the printingplatform.

Optionally, the method comprises scraping excess building material offthe roller with the scraper, and shifting the scraper in the indexingdirection after leveling a pass in a layer.

Optionally, the method comprises offsetting the scraper's position inthe indexing direction for printing different layers.

Optionally, the method comprises collecting the building materialscraped off the roller into the trough, and shifting the trough in theindexing direction after leveling a pass in a layer.

Optionally, the method comprises removing the building materialcollected in the trough from at least two positions along a length ofthe trough.

Optionally, the method comprises pumping the building material collectedin the trough from above the trough.

Optionally, the printing platform, the roller, the scraper and thetrough move together in the printing direction while dispensing thebuilding material.

Optionally, the method comprises increasing the space between theprinting platform and a tray on which the object is printed prior toprinting a subsequent layer.

An aspect of some embodiments of the present invention is the provisionof a raster scanning 3-D printing system comprising a printing platformmounted on a Y rail movable in a printing direction and in an indexingdirection, the printing platform comprising a printing head configuredfor dispensing building material while moving in a printing directionone pass at a time, and layer by layer, a roller configured for levelingthe dispensed building material one pass at a time, a scraper configuredfor scraping excess building material off the roller, and a troughconfigured for collecting the building material scraped off the roller,wherein the printing platform moves in the indexing direction along theY rail, and wherein both the Y rail and the roller extend over allpasses of the printing system and are stationary in the indexingdirection.

Optionally, at least one of the scraper and the trough are movable inthe indexing direction.

Optionally, at least one of the scraper and the trough extend over allpasses of the printing system and are stationary in the indexingdirection.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are described herein by way of exampleonly, with reference to the accompanying drawings. With specificreference to the drawings in detail, it is stressed that the particularsshown are by way of example and for purposes of illustrative discussionof embodiments of the invention. In this regard, the description takenwith the drawings makes apparent to those skilled in the art howembodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a schematic illustration of a known 3-D printing systemincluding a printing platform supported by a two rail system, one railabove the other;

FIG. 2 is a schematic illustration of ridges formed on the 3-D printedobject due to misalignment between a roller on a printing platform and atray;

FIG. 3 is a schematic illustration of a 3-D printing system including aroller that extends along a dimension of the tray according to someembodiments of the present invention;

FIG. 4A is a schematic illustration of a roller unit including a roller,a scraper and a waste collection trough according to some embodiments ofthe present invention;

FIG. 4B is a schematic illustration of a waste disposal unit including ascraper, waste collection trough, waste pipe and waste pump according toembodiments of the present invention;

FIG. 5A is a schematic illustration of a 3-D printing system including ascraping blade that extends over one pass and a roller that extends overa dimension of a tray according to some embodiments of the presentinvention;

FIG. 5B is a schematic illustration of a 3-D printing system including aroller having a length that covers one pass and is rotatably supportedon an axle that extends over a dimension of a tray according to someembodiments of the present invention;

FIG. 5C is a schematic illustration of a 3-D printing system including aroller having a length that covers one pass engaged on a printingplatform that is supported on a rail that extends over a dimension of atray according to some embodiments of the present invention;

FIG. 6 is a schematic illustration of a 3-D printing system including aprinting platform supported on opposite ends by rails aligned with theprinting direction according to some embodiments of the presentinvention;

FIG. 7 is a schematic illustration of a 3-D printing system including aprinting platform supported on opposite ends by rails aligned with theindexing direction according to some embodiments of the presentinvention; and

FIGS. 8A and 8B are schematic illustrations of a casing for a 3-Dprinting system including options for doors in the casing according toembodiments of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to SFFsystems and more particularly but not exclusively to raster scanning 3-Dprinting systems. The inventors have found that during raster scanningof multiple passes in a printed layer, inconsistencies in the levelingof the passes may occur, resulting in ridges forming at the bordersbetween passes. Typically the ridges form due to inaccurate alignment ofthe roller with respect to the tray such that the roller is not parallelto the tray. Adjusting the roller to maintain a parallel alignmentbetween the roller and the tray is typically a cumbersome and timeconsuming procedure.

For purposes of better understanding some embodiments of the presentinvention, as illustrated in FIGS. 3-8 of the drawings, reference isfirst made to the construction and operation of a known printing systemas illustrated in FIGS. 1 and 2. It is noted that while the prior artsystem is known, the present inventors have discovered the source of theproblem described below as well as the methodology of solving it.

Reference is now made to FIG. 1 showing schematic illustration of aknown printing system including a printing platform supported by a tworail system on one end of the printing platform. Known printing system100 typically includes printing platform 110 supported on a two X railsystem 120, one rail above the other in the Z direction. Printingplatform 110 including the roller unit 107 is typically supported onlyon one end by two rail system 120 aligned with the printing direction (Xdirection). The two rail system, one over

the other, serves to increase the stability and stiffness of theprinting platform and its components in the vertical direction (Zdirection). While printing, the printing platform advances along aprinting direction (X direction) as it dispenses material from printinghead(s) 105 via one or more printing nozzles 106, levels the dispensedlayer with roller unit 107 and cures it with one or more curing lamps108.

Upon completion of a first pass 131, the printing platform together withits supporting rail system 120 is shifted along the Y rails 130 in theindexing direction (Y direction) to print a subsequent pass 132 andcontinues until completing a layer of the object 160. One or more motorsmay be used to control motion of the printing platform and/or the tworail system along an area defined by a tray 150 supporting the printedobject 160.

Typically, tray 150 is movable in the vertical direction (Z direction).One or more motors may be used to control motion of the tray and adjustits height for each layer being printed. For example, at an initialstate the tray may be positioned closest to the printing platform andafter each layer printed the tray may be lowered in the Z direction apredefined distance with respect to the printing platform, toaccommodate printing of the subsequent layer.

Typically, each printed layer is accompanied by an offset of theprinting head in the indexing direction (Y direction). This offsetand/or shift facilitates preventing accumulation of defects in aspecific area that may be brought about by defective nozzles, from layerto layer. This technique is typically referred to as nozzle scattertechnique and is described in greater detail in incorporated U.S. Pat.No. 6,259,962.

The inventors have found that stability and stiffness in the verticaldirection (Z direction) with respect to the tray is critical in assuringproper leveling of the layer. When the stability and stiffness of theroller is not sufficient, roller oscillations in the Z direction mayappear during printing. Oscillations may result in a wavy appearance ofthe top surface of the layer along the printing direction (Z direction),and when strong oscillations occur, printing may automatically ormanually be halted. Strong oscillations are typically triggered byfluctuating forces that the wavy layer may exert on the roller. Theinventors have found that although the printing platform is firmlyattached to the two rail system, and the rails are hard, the structureis not sufficiently stable and stiff. Particularly, the oppositelongitudinal end of the roller which is not attached to the two railsystem is not stable.

Reference is now made to FIG. 2 showing a schematic illustration ofridges formed on the printed object due to misalignment between a rollerand/or printing platform and a tray. Although roller 107 should beparallel to Y rails 130 and tray 150, the printing platform 110 andhence the roller tends to tilt, resulting in protrusions and/or ridges205 where each protrusion or ridge corresponds to one pass e.g. pass131, pass 132, pass 133. The adjustment procedure to realign theprinting platform so that the roller remains parallel to the Y rails andtray 150 may be cumbersome and difficult.

According to some embodiments of the present invention, the 3-D printingsystem includes a roller supported on two opposite ends with one or morerails. The inventors have found that by replacing the known two rails,one above the other to support the printing platform on one end, withone or more single rails supporting the printing head and/or roller ontwo opposite ends increases stability and stiffness of the roller. Theinventors have also found that supporting the printing platform and/orroller from two opposite ends provides consistent vertical alignmentbetween the tray and the roller and thus avoids formations of ridgesbetween passes. If formation of ridges may be avoided in this manner,the previous requirement for a high degree of parallel alignment betweenthe roller and the tray is prevented. According to some embodiments ofthe present invention, consistent vertical alignment between the trayand the roller is achieved by maintaining a single axis about which theroller is rotated for all passes. The inventors have found thatconsistent vertical alignment between the tray and the roller may beachieved by supporting the roller on an axle extending over the entiretray and supporting the axle on both ends. In some exemplaryembodiments, the roller is rotatably mounted on a roller axle such thatthe roller axle extends over the entire tray and is supported on bothends. In some exemplary embodiments, the roller extends over the entiretray and is physically held by two bearings at both ends of the roller,wherein the bearings are centered at the roller axis and are held byrespective carriages.

Typically the printing platform is movable along the one or more railssupporting the printing platform, and the one or more rails supportingthe printing platform is movable along the two additional rails coupledto it in a perpendicular direction, so that movement in two dimensions(X and Y) may be easily achieved.

According to some embodiments of the present invention, the rail systemincludes one rail aligned with the indexing direction to support theprinting platform. In some exemplary embodiments, the roller unit isdirectly supported by the rail aligned with the indexing direction andthat rail is coupled on each end to a rail aligned with the printingdirection. In some embodiments of the present invention the roller unitis extended over a dimension of the tray, e.g. width or length of thetray, providing substantially consistent leveling over all passes in alayer. In some exemplary embodiment, the roller is extended over adimension of the tray, while the scraper and/or waste trough ismaintained over a width of a single pass and is advanced with theprinting platform to each additional printing pass.

According to some embodiments of the present invention, the roller unitis supported on the printing platform and the printing platform issupported on two rails, each one at an opposite end of the printingplatform. In some exemplary embodiments, the printing platform issupported on two rails aligned in the indexing direction. In otherembodiments of the present invention, the printing platform is supportedon two rails aligned in the printing direction.

According to some embodiments of the present invention, the size of the3-D printing system is reduced by eliminating a requirement for a doublerail support on one end of the printing head. In some exemplaryembodiments, the height of the 3-D printing system is reduced.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

Reference is now made to FIG. 3 showing a schematic illustration of aprinting system including a roller that extends along the length of thetray according to some embodiments of the present invention. The presentinventors have found that although proper leveling of the layers issensitive to misalignment of the printing platform with the tray, otherprinting activities such as curing and dispensing are less sensitive tomisalignment. According to some embodiments of the present invention, aroller 307 is as long in the Y direction and/or indexing direction asrequired for covering the Y dimension of tray 150 and/or object 160.

In some exemplary embodiments, roller 307 and printing platform 310 aresupported on Y rail, while Y rail 330 is coupled on both ends to X rails320. In some embodiments of the present invention, roller 307 is held bytwo bearings at both ends of the roller, wherein the bearings arecentered at the roller longitudinal axis. According to some embodimentsof the present invention, printing platform 310 is mounted on Y rail 330using any of various methods and devices known in the art so that theprinting platform is supported and moveable along Y rail 330. Any ofvarious motors and/or actuators and devices for their control known inthe art may be used to move and accurately control motion of printingplatform 310 along Y rail 330. In some exemplary embodiments, roller 307is supported on its longitudinal axis so that it is rotatable. In someexemplary embodiments, rotation of roller 307 is provided by a motor.

The Y rail 330 is mounted at both ends to a carriage 350 which supportsthe Y rail and couples it to two X rails 320 on both ends of Y rail 330so that the Y rail may be moved along the X rails. Any of various motorsand/or actuators and devices for their control known in the art may beused to move and control motion of carriages along the X rails, e.g. astep motor with a linear encoder may be used and/or piezoelectric motor.

According to some embodiments of the present invention, a system 300equipped with roller 307 extending over the length of the tray andsupported on both of its ends facilitates consistent leveling acrosspasses of a layer e.g. passes 131, 132, etc., as well as a sufficientlystable and stiff structure. In exemplary embodiments of the presentinvention, the structure of printing system 300 does not requireperiodic adjustment of the alignment between the printing platform andthe tray or supporting rails to maintain acceptable alignment betweenthe roller and the tray or supporting axis. In fact, a high requirementto maintain parallel alignment is not required for roller 307, since theroller is not shifted in the indexing direction from pass to pass.Therefore, even if the roller is positioned at an angle with respect tothe tray, ridges 205 (FIG. 2) may not be formed on borders betweenpasses due to leveling by the roller.

Reference is now made to FIGS. 4A and 4B showing a schematicillustration of a roller unit including a scraper and a waste collectiontrough according to some embodiments of the present invention. Accordingto some embodiments of the present invention, roller 307 is rotatablymounted on a roller axle 333. In some exemplary embodiments of thepresent invention, roller axle 333 is supported on both ends to carriage350 or Y rail 330 using a bearing 308 on each end of the roller axle. Insome exemplary embodiments, the roller axle is not required and thebearings are centered at the roller's longitudinal axis.

Typically, a scraping blade 420 is implemented to scrape clean roller307 of excess printing material which the roller accumulates whileleveling the printed layers. The scraped material is typically collectedby collection trough 430. Typically, the trough is very close to theupper surface of the printed object and therefore a gravitational drainof the waste from the trough may not be possible and/or practical.According to embodiments of the present invention a pump 435 is used topump off the waste in upward direction via a waste pipe 434. The pumpedwaste is collected in a waste container. According to some embodimentsof the present invention, the waste collection trough 430 and scrapingblade 420 associated with roller 307 may be extended along the length ofroller 307, e.g. the roller unit may be extended over the length of thetray. As such the length of roller corresponding to the summation of thewidths of all the passes is scraped when leveling each of the passes.

Reference is now made to FIG. 5A showing a schematic illustration of aprinting system including a scraping blade that covers one pass and aroller that extends over the width of the tray according to someembodiments of the present invention. According to some embodiments ofthe present invention, scraping blade 502 of the roller unit may beconfined and/or reduced to a width corresponding to the width of asingle pass and/or the width of the printing platform 509 and may beshifted from pass to pass together with the printing platform to clearmaterial leveled a single pass and/or to scrap material off the rollerover a length less than the entire length of the roller. In someexemplary embodiments, the waste collection trough extends over thelength of the roller and the waste collection trough and roller are notshifted in the indexing direction with printing platform 509.

Typically, the scraping blade is pressed tightly to the roller, inducingfrictional torque on the roller. The length of the scraping bladedirectly affects the torque generated on the roller. The presentinventors have found that by reducing and/or minimizing the length ofthe blade, the cost of the blade as well as cost and size of the rollermotor required may be reduced.

Typically the quality of the blade tends to deteriorate, e.g. becomesscratched from over use due to continuous frictional contact with therotating roller. This may occur even when the blade is made of a toughmaterial such as stainless steel. Scratches on the blade may lead tosmall amounts of printing material passing under the blade and remainingon the roller. Printing quality typically deteriorates as a result ofmaterial left on the roller. Typically, due to over use, the blade mayneed to be replaced. In some exemplary embodiments, a shorter blade mayfacilitate reducing maintenance costs when replacing the blade.

According to some embodiments of the present invention, it may beadvantageous to use a short waste collection trough, e.g. extending overone pass. Typically, the wasted collected in the trough does not easilyflow. A long trough extending over the width of a layer and/or tray mayrequire 2-3 or more waste pumps to pump the waste from the trough at 2-3or more points along the indexing direction. In some exemplaryembodiments, the waste collection trough is confined to a widthcorresponding to a single pass and/or to the width of the blade and isshifted along the indexing direction together with printing platform310. In some exemplary embodiments both the scraping blade and troughare confined to the width corresponding to a single pass and are shiftedwith the printing platform from pass to pass.

According to embodiments of the present invention, the nozzle scatteringtechnique may be applied to scraper 420 so that the scraper may beoffset together with printing head 108 in the indexing direction whenprinting different layers. The inventors have found that defects on thescraper, e.g. scratches on the scraper edge, may lead to slight defects,i.e., negligible defects, in a printed layer. However, when printingmultiple layers, the defects may accumulate and become significant. Byfacilitating offsetting of the scraper in the indexing direction fordifferent printed layers, the accumulated effect of defects in levelingmay be avoided.

The inventors have also found that by facilitating relative motionbetween the scraper and the roller for different layers, wear on theroller due to defects on the scraper may be more evenly distributedalong the roller. Such motion may avoid formation of scratches on theroller in discrete locations over time and/or operation of the printer.

Reference is now made to FIG. 5B a schematic illustration of a printingsystem including a roller having a length that covers one pass androtatably supported on a roller axle that extends over the width of thetray according to some embodiments of the present invention. Accordingto some embodiments of the present invention, printing platform 510 androller 507, e.g. roller axle, are supported on Y rail 330 using any ofvarious methods and devices known in the art so that the printingplatform and roller 507 are supported and moveable along Y rail 330.Roller axle 333 (FIG. 4A) is supported on both ends to carriage 350 or Yrail 330 and runs parallel to Y rail 330. The Y rail 330 is mounted atboth ends to a carriage 350 which supports the Y rail and couples it totwo X rails 320 on both ends of Y rail 330 so that the Y rail may bemoved along the X rails. According to embodiments of the presentinvention, Y rail 330 is aligned perpendicular to the X rail.

Typically, three conditions should be met in order to facilitate aconsistent leveling surface over all passes of each layer: a. Roller 507is engaged on Y rail 330 supported on both ends, in a way that theroller is precisely parallel to Y rail with respect to the verticaldirection (Z axis), b. Rail Y is rigid with respect to bending in Zdirection, and c. Y rail 330 is supported on two X rails at both ends ofthe Y rail. According to embodiments of the present invention, even if Yrail 330 is not precisely perpendicular to X rail or to Z rail (Z railis the rail along which the tray moves) or to the surface of the tray,said consistency of leveling surface over all passes is maintained.

Reference is now made to FIG. 5C showing a schematic illustration of aprinting system including a roller having a length that covers one passengaged on a printing platform that is supported on a rail that extendsover the width of the tray according to some embodiments of the presentinvention. According to some embodiments of the present invention,roller 508 is supported on printing platform 511. According toembodiments of the present invention, printing platform 511 is supportedon Y rail 330 using any of various methods and devices known in the artso that the printing platform is supported and moveable along Y rail330. The Y rail 330 is mounted at both ends to a carriage 350 whichsupports the Y rail and couples it to two X rails 320 on both ends of Yrail 330 so that the Y rail may be moved along the X rails. According toembodiments of the present invention, Y rail 330 is aligned in the Yaxis so that it is parallel to the Y axis. According to some embodimentsof the present invention, roller 508 engaged on printing platform 511which in turn is supported on Y rail 330, facilitates maintaining aconsistent leveling surface over all passes of each layer, even if Yrail is held at a slight angle with respect to the vertical direction (Zaxis). The configuration depicted in FIG. 5C provides similar stability,stiffness, and leveling performance as described in reference to FIG.5B. In some exemplary embodiments of the present invention, printingplatform 511 is supported on the Y rail along the width of the printingplatform to provide stability and stiffness to the structure.

Reference is now made to FIGS. 6 and 7 showing additional configurationsfor a printing system including two rails supporting the printingplatform from opposite ends, according to some embodiments of thepresent invention. In FIG. 6, printing platform 610 is supported by twoX rails 620 on each side of platform 610. The X rails 620 are mounted atboth ends to carriages which support the X rails and couples them to twoY rails 630 at both ends of X rails 620 so that the X rails may be movedalong the Y rails.

In FIG. 7 printing platform 710 is supported by two Y rails 730 atopposite ends of platform 710. The Y rails 730 are mounted at both endsto carriages which support the Y rails and couple them to two X rails720 at both ends of Y rails 730, so that the Y rails may be moved alongthe X rails.

According to embodiments of the present invention, additional stabilityis achieved by adding an additional rail on an opposite end of theprinting platform, so that additional stability is added to the entireprinting platform and not only to the roller. According to embodimentsof the present invention, improved stability and stiffness to the entireprinting platform is provided by implementing a rail system with 4 rails(FIGS. 6 & 7). According to other embodiments of the present invention,improved stability and steadiness of the roller is provided with a railsystem including 3 rails (FIGS. 3-5).

According to embodiments of the present invention, there is provided ashallower and more compact design of the printing system with addedstability as compared to prior art systems. According to embodiments ofthe present invention, a shallower and more compact design is providedby replacing the two rail system, one rail above the other in the Zdirection by a single rail system. In other exemplary embodiments, ashallower more compact design is provided by replacing the two railsystem, one rail above the other in the Z direction by a two rail systemon either end of the printing platform. In some exemplary embodiments,the printing systems described herein provide a relative height of therails in the vertical direction (Z direction) that is lower than otherknown systems.

Reference is now made to FIGS. 8A and 8B showing schematic illustrationsof casings for a printing system including options for doors in thecasing according to embodiments of the present invention. According toembodiments of the present invention, object 160 may be removed form thecasing 900 when the tray 150 is positioned at its lowest Z point. Insome embodiments of the present invention, door 920 may be positioned onone side of the casing and the object may be removed sideways (FIG. 9A).In some exemplary embodiments, the door may be positioned at a lowerlevel of the casing. According to other embodiments of the presentinvention, door 930 may be further extended to include also a top cover(FIG. 9B) so that two surfaces of the casing are lifted to remove theobject, e.g. with a hinge on an upper surface of the casing. In someexemplary embodiments of the present invention, this design may providemore accessibility to the object and printing system and may be usefulwhen maintenance is required.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

What is claimed is:
 1. A system comprising: a printing platformcomprising: a printing head configured to dispense building material asthe printing platform is advanced in a printing direction one pass at atime, and layer by layer, wherein at least one layer includes multiplepasses; and a roller rotatably mounted on the printing platform, theroller configured for leveling the dispensed building material one passat a time; a pair of Y rails along which the printing platform includingthe roller is configured to shift in the indexing direction prior to theprinting head dispensing a subsequent pass of a layer, wherein the pairof Y rails extend in the indexing direction, are displaced from oneanother in the printing direction and are at a same height in a Zdirection, the indexing direction perpendicular to the printingdirection and the Z direction; and a pair of X rails along which the Yrails are configured to advance in the printing direction, wherein thepair of X rails extend along the printing direction and are displacedfrom one another in the indexing direction.
 2. The system according toclaim 1, wherein a first end of the printing platform in the printingdirection is supported on a first Y rail of the pair the Y rails and asecond end of the printing platform in the printing direction issupported on a second Y rail of the pair of the Y rails.
 3. The systemaccording to claim 1, wherein the pair of the Y rails are stationary inthe indexing direction.
 4. The system according to claim 1, wherein thepair of the Y rails extends over all passes of the system.
 5. The systemaccording to claim 1, wherein the pair of the X rails are stationary inboth the printing direction and the indexing direction.
 6. The systemaccording to claim 1, wherein the printing platform is supported andcoupled to each of the Y rails with a first carriage.
 7. The systemaccording to claim 1, wherein each of the Y rails is supported andcoupled to each of the X rails with a second carriage.
 8. The systemaccording to claim 1, wherein the printing platform comprises at leastone curing lamp configured to cure the building material that isdispensed.
 9. The system according to claim 8, wherein the printingplatform comprises a pair of curing lamps and wherein the printing headis between the pair of curing lamps.
 10. The system according to claim1, wherein the printing platform comprises: a scraper configured forscraping excess building material off the roller; and a troughconfigured for collecting the building material scraped of the roller.11. The system according to claim 1, comprising a tray configured tosupport the dispensed building material at a defined height, wherein thetray is movable in the Z direction.
 12. The system according to claim 1,wherein the system is configured to build a three dimensional object.